Wind turbines have long been used to convert the kinetic energy of wind into mechanical energy that drives a generator, thereby producing electricity. Over time, there has been a significant increase in the overall size of these machines because of the desire to capture more of the wind's available energy. Nevertheless, there remain sites better suited for smaller wind turbines due to their wind conditions, local restrictions, or other limiting factors. A great variety of wind turbine sizes now exist as a result, which makes handling their components very challenging particularly in terms of transportation and storage.
For example, many wind turbine towers are assembled from annular sections of rolled steel. The sections are welded together at a factory to form cylindrical or conical tubes. The tubular sections are then transported to the intended wind turbine site and joined together by flange connections provided on their ends. The size of these components varies depending on the size of the particular tower being built and their location within that tower. Diameters, for example, may range from approximately 2 to 5 meters. Additionally, the intended sites are often located far away from the tower factories, meaning that the tower sections are often handled several times before reaching the sites. The handling could be unloading from a transportation vehicle to storage (or vice-versa), the transfer from one form of transportation to another (e.g., land to sea), etc.
WO 2007/093854 discloses one solution to address these challenges. The solution involves a tower stacking system having a fixture (“foot”) that can be mounted to an end of a tower section at a manufacturing site. The fixture can remain fixed to the tower section until the intended site of the wind turbine, facilitating the various handling steps along the way. To accommodate different sizes of tower sections, the fixture incorporates sloped surfaces to guide the tower section towards the fixture's center when placed thereon. A central locking element can be moved vertically to match up with the resting place of the tower flange relative to the sloped surfaces. Locking elements on each side of the central locking element are also adjustable to match up with the tower flange. Eventually the locking elements are each secured to the tower flange.
The locking elements in the '854 application are shown as disc-like elements whose movements are guided by slots in the fixture. Each can be bolted to the tower section when a hole through them is aligned with a bolt hole in the flange of the tower section. But the '854 application also mentions the possibility of using clamps to connect to the tower section. Indeed, WO 2010/012280 discloses one embodiment of this principle. The locking elements in that application are movable clamps that grip the tower flange.
Although this type of solution has proven satisfactory for some purposes, wind turbine manufactures are still seeking new ways to address the above-mentioned challenges to further improve handling and reduce costs.